In science, Alexis Thérèse Petit (1791-1820) was a French physicist noted for his 1818 publication on the efficiencies of air-engines and steam-engines and for his 1817 work with French physicial chemist Pierre Dulong in the correction of Newton's law of cooling. [1] More notably, in 1819 they discovered that the specific heat of any solid element multiplied by its atomic weight is approximately equal to a constant. [2] This has come to be known as the Dulong-Petit law for the specific heat capacity of metals.

Education
Petit studied at the École Polytechnique, graduating in 1811, later becoming professor of physics from 1815 to 1819.

Influence
In the history of thermodynamics, Petit is known to have had a discussion with French physicist Sadi Carnot on the subject of efficiency in engines, which may have influenced or stimulated the latter in his 1824 Reflections on the Motive Power of Fire, with its famous derivation of the efficiency of heat engines in general. One of Petit’s noted students in physics, during the years 1815-16, was Auguste Comte, the French sociologist and philosopher who is generally credited with having coined the term sociology and who first outlined the subject of "social physics". Physics, for Comte, was his most difficult class, because, in his own words, Petit "went too fast". [3]

References
1. Whewell, William. (1866). History of the Inductive Sciences, (section: “Correction of Newton’s law of cooling”, pgs. 149-50). Appleton.
2. Scerri, Eric R. (2007). The Periodic Table: its Story and its Significance, (pgs. 59-60). Oxford University Press.
3. Pickering, Mary. (1993). Auguste Comte, (pg. 24). Cambridge University Press.